An integrated circuit (IC) device, such as a microprocessor, may include circuitry comprised of many types of discrete circuit components, including transistors, resistors, and capacitors, as well as other components. Semiconductor manufacturers are subject to ever-increasing pressure to increase the speed and performance of such IC devices while, at the same time, reducing package size and maintaining reliability. Thus, by way of example, a modern microprocessor may comprise a die including literally millions of closely-spaced transistors and other discrete components exhibiting sub-micron dimensions and operating at clock rates exceeding 1 GHz. As a result, these microprocessors exhibit high power dissipation and, hence, a corresponding heat load requiring increased cooling capacity, and these high cooling requirements are pushing conventional thermal management technology to its limit.
The power consumption of a microprocessor, as well as other types of IC devices, is generally proportional to the operating frequency and the number of transistors required to perform the applications or instructions being executed. The heat generated within a die as a result of this power dissipation must be properly transferred away from the die. If adequate heat transfer does not occur, the die temperature may achieve a level at which performance and reliability suffer or can no longer be guaranteed and, if unchecked, a die temperature may be reached at which permanent structural damage to the microprocessor occurs.
The power dissipation of a microprocessor may, however, cause uneven heating of the die. Because one application may primarily utilize one portion of the microprocessor circuitry—i.e., a functional unit, such as an arithmetic and logic unit—while another application may primarily utilize a different functional unit, vastly different amounts of heat may be generated on the die at various locations. Thus, for a particular application, a microprocessor or other IC device may exhibit high temperature locations, or “hot spots,” corresponding to die locations proximate one or more functional units experiencing a high workload. Also, with the advent in recent years of microprocessors possessing high speed and performance, there has been increasing disparity between typical power—i.e., the power consumed when running normal applications, such as those run on a personal computer—and maximum power—i.e., the power consumed while running a synthetic, high-power workload specifically designed for maximum power consumption. Thus, although a microprocessor may rarely, if ever, achieve maximum power for an extended period, techniques for thermal management of microprocessors may, in some instances, target the maximum power level to insure that die temperatures will not exceed thermal design limits during operation, potentially causing heat-induced failure or damage to the microprocessor.
As is suggested above, thermal management is a critical aspect of the design of modern microprocessors, as well as other IC devices. To remove heat from a semiconductor die, it is known in the art to couple a passive heat transfer device to the die. For example, it is common to thermally couple a heat sink or heat pipe, or other liquid cooling element, to a semiconductor die; however, such passive components possess a limited capacity to dissipate heat. Heat removal may also be facilitated by an active heat transfer device such as a fan, which are often employed in combination with a heat sink having a large surface area (e.g., a plurality of fins). There are, however, several disadvantages associated with the use of fans for cooling IC devices, including poor reliability compared to semiconductor devices, noise, and space requirements. Also, active devices such as fans, as well as the above-described passive device, are generally over-designed for typical power dissipation in order to address the worst case scenario—i.e., the dissipation of maximum power.
Another approach to thermal management of an IC die is to actively monitor the temperature of the die. Early thermal monitoring systems consisted of a temperature sensor attached to a heat sink, the heat sink being coupled with a die. If the sensor detected some predetermined threshold temperature, off-chip control hardware and software initiated a response, generally the switching of power to a fan or a reduction in clock frequency. Such thermal monitoring systems are inherently inaccurate due to poor thermal coupling (i.e., a thermal time delay) between the sensor and die. Also, the off-chip control hardware requires the addition of other components to the IC device being sensed or to the next-level assembly, and these added components may consume more surface area in the next-level assembly (i.e., surface area of a circuit board) than the IC device itself.
More recently, manufacturers have introduced on-chip thermal sensors that are fabricated directly on a semiconductor die. Although on-chip thermal sensors substantially eliminate the inherent latency of the separately-attached thermal sensor, currently available sensor control and interface logic does not provide reliable temperature measurement and/or closed-loop thermal control. A lack of integration amongst the various elements comprising the conventional sensor control and interface logic, as well as poor integration with the IC device itself, provide a thermal management system exhibiting insufficient response time and, hence, unreliable temperature control.
Semiconductor manufacturers have also turned to lower supply voltages to reduce power dissipation of IC devices. However, the increasing speed and circuit density of newer microprocessors will necessitate even lower supply voltages, but the electrical noise generally present in any system inherently limits the degree to which supply voltages may be further reduced.
Accordingly, there is a need in the art for an integrated thermal management system and method of use for microprocessors and other IC devices providing reliable on-chip, closed-loop temperature control.